We present accidental findings that potassium channel blockers, such as tetraethyl-ammonium (TEA) or 4-aminopyridine (4-AP), inhibit the sustained tonic contraction induced by carbachol in rat detrusor muscle strips. The relatively lower concentrations (<2 mM) of TEA and 4-AP inhibited phasic and tonic contractions induced by 5 micrometer carbachol, whilst the relatively higher concentrations of TEA and 4-AP (>5 mM) potentiated phasic contractions. The potentiation of phasic contraction was not observed in nicardipine pretreated condition. In nicardipine pretreated condition, the concentration-response curves for the negative inotropic effect of potassium channel blockers were shifted to the right by the increasing concentration of carbachol from 0.5 micrometer to 5 micrometer. IC50 was changed significantly from 0.19 to 0.64 mM (TEA) and from 0.21 to 0.96 (4-AP). Such inhibitory effects were also observed in Ca2+ depleted condition, where 0.1 mM EGTA and 1 micrometer thapsigargin were added into Ca2+ free solution. In conclusion, inhibitory effects of potasssium channel blockers on carbachol-induced contraction may be ascribed to the direct inhibition of receptor-agonist binding.
4-Aminopyridine/pharmacology ; Animals ; Bladder/metabolism ; Calcium/chemistry/metabolism ; Calcium Channel Blockers/pharmacology ; Carbachol/*pharmacology ; Dose-Response Relationship, Drug ; Female ; Guinea Pigs ; Inhibitory Concentration 50 ; Male ; Mice ; Muscle Contraction/*drug effects ; Muscles/drug effects/metabolism/*pathology ; Nicardipine/pharmacology ; Potassium Channel Blockers/*pharmacology ; Protein Binding ; Rabbits ; Rats ; Rats, Sprague-Dawley ; Support, Non-U.S. Gov't ; Tetraethylammonium/pharmacology ; Vasodilator Agents/pharmacology

OBJECTIVETo study the possibility of metallothionein (MT) participating in the process of ischemia/reperfusion protection.

METHODSThe model of pig latissimus dorsi island flap and cultured myocytes were used in this study. The island flap was preconditioned with ischemia and the cultured myocytes were treated with anoxia. MT was detected in the flap and the cultured myocytes instantly and at 12 and 24 hours after the treatment. The protection effect of precondition on flap ischemia/reperfusion damage was observed by recording flap necrosis and the serum LDH level. The protection effect of precondition on myocyte anoxia/reoxygenation damage was observed by recording the cell survival rate and MDA content. The change in the protection effect was also observed after the MT was inhibited by PD098059.

RESULTSThe content of MT in cultured myocytes increased obviously 12 hours after precondition. Similar result was observed in flap tissue 24 hours later. Compared with the non-conditioned flap, the necrosis areas of the preconditioned flaps were smaller, the serum LDH was lower. The survival rate of preconditioned cultured myocytes was higher compared with non-conditioned cells (P < 0.05). The content of MDA and the quantity of discharged LDH were less (P < 0.05). When MT was inhibited by PD098059, the delaying protection of precondition disappeared. The observed quotas at that time were the same with those of simple I/R or A/R groups (P > 0.05).

CONCLUSION24 hours after precondition, the flap and the cultured myocytes are protected from re-damage of I/R or A/R. MT is involved in this process.

Animals ; Cell Hypoxia ; physiology ; Cell Survival ; physiology ; Cells, Cultured ; Enzyme Inhibitors ; pharmacology ; Flavonoids ; pharmacology ; Ischemic Preconditioning ; L-Lactate Dehydrogenase ; blood ; metabolism ; Malondialdehyde ; metabolism ; Metallothionein ; drug effects ; metabolism ; Muscles ; cytology ; metabolism ; surgery ; Necrosis ; Reperfusion Injury ; metabolism ; Surgical Flaps ; pathology ; Swine ; Time Factors